Some third-level colleges are delaying the entry of first years by a further week after confirmation that Leaving Cert results and Central Applications Office (CAO) offers won't be released until September.
The country's largest university, University College Dublin (UCD), said it will affect its plans to have Orientation Week for first years starting on September 14.
"We anticipate it will impact on these students and are seeking to minimise this for them," a UCD spokesperson said.
At Trinity College Dublin, Freshers' Week is being put back a week to September 28, with the start of the first year teaching term also back a week, to October 5.
Technological University Dublin is delaying Orientation Week to September 28, with lectures for first years starting on October 5.
Dublin City University, which had planned a two-week orientation programme for first years starting September 21, said it will have to curtail that.
The disruption to the 2020 Leaving Cert prompted all third-level colleges to pencil in later starting dates, and the publication this week of the September timeline for the results and CAO offers forced a further review.
Maynooth University and the University of Limerick (UL) are sticking with their re-opening schedules. Maynooth's Orientation Week will start on September 21, with lectures beginning the following week.
UL is also going ahead with its existing plans to bring first years on to campus on September 28.
Leaving Cert results will issue on September 7, three weeks later than usual, and CAO round one offers will follow on September 11. Round two offers will issue on September 23 and, depending on the college, acceptance of a place may mean a slightly later start for those students.
The late release of the results and offers has sparked some criticism. Union of Students in Ireland president Lorna Fitzpatrick said the delay in issuing Leaving Cert results was unfair on students hoping to start third-level, who had already faced so much change and uncertainty.
"The turnaround time between the results coming out, offers being made and college starting is now extremely short, which heaps yet more pressure on students," she said.
Further and Higher Education Minister Simon Harris moved to assure students grant payments would not be affected by the delay.
Meanwhile, the CAO offer season kicks off today with offers to 5,800 applicants, mainly mature and deferred applicants.